Fighter5347 over on the Unreal Engine forums released a free Foliage Pack

I having trouble using these with the UT4 editor however. I can see all the materials and meshes in the editor, but as soon as I try to use them, they default to the world grid material. Any ideas how to make them work?

Make sure the path (under the UT Editor's Content folder) you install the assets in is exactly the same as it was in UE4. If you have the UE4 editor installed too, probably the simplest way to do that (and the way I always do it now) is just run UE4 and use "migrate" to copy the assets to the exact same folder hierachary under the UT4 Editor Content path.

If you've already tried to install them in the wrong path there could be bad redirectors left behind screwing things up even after you've put things in the right place. Try using "fix redirectors" if you think that might be happening (worked for me once with Ripper assets).

Also the further apart the engine versions used by the UT Editor and UE4 Editor are the more likely there might be some problems with things not working.